A standard detonator is usually in the form of a tubular stick filled with a detonating composition of flammable material in which an ignitor device is embedded for the purpose of reacting when powered with electricity. The ignitor device can be a resistance which transforms electricity into heat, two electrodes between which electricity is transformed into an arc passing through the flammable material, or through a suitable dielectric, . . . At one of its ends, the cylindrical stick thus has two electrical conductors enabling it to be connected to an external source of electricity.
Nowadays, the use of pyrotechnics, e.g. in mining or quarrying for destroying a natural obstacle, or for demolishing a structure, . . . requires more and more elaborate blasting plans drawn up and executed by computers and microprocessors for processing data.
In this type of application, xe2x80x9celectronic delayxe2x80x9d detonators are used which include an electronic circuit with a microcontroller enabling information to be exchanged with a central unit controlling blasting and via which an electrical energy storage device is charged, and then discharged into the flammable material with a certain programmed delay.
Such electronic delay detonators have been in existence for many years. They are in the form of a one-piece product, the electronic portion being associated on manufacture with the explosive portion.
This one-piece characteristic gives rise to major constraints associated with the explosive material of the detonator. Strict regulations govern all the steps in the life of such a product, and in order to be satisfied this requires expensive procedures to be implemented during manufacture, handling, and transport (special packaging). In addition, the transport of such products by air is authorized only with special packaging that is very expensive and that has been approved by the appropriate national authorities.
Canadian document No. 2 132 148 published on Mar. 16, 1996 describes a detonator with an electronic pilot made up of two portions that can be manufactured separately and that possess means enabling them to be finally assembled together merely by engaging the explosive portion in the electronic portion. Nevertheless, the device described in that document suffers from numerous drawbacks concerning both manufacture of the electronic pilot and final assembly of the electronic portion with the explosive portion, particularly on site. The electronic module is embedded in a resin which presents at least one outwardly-open cavity with a very small female connector formed in the bottom thereof, and during manufacture it is very difficult to guarantee that the connector will conduct electricity. Furthermore, the nature of the conductors available at the outlets of standard detonators on the market do not make it possible to be sure that the end has been properly plugged into said connector without making adaptations to the conductors, which would require action to be taken on the detonators needing to be performed under the conditions specified by the regulations applicable to the presence of explosives, i.e. conditions that are expensive.
Document EP 0 843 807 describes an electronic delay detonator in which the body of the electronic module is assembled with the detonator by means of a snap-fastenable cap without giving other details as to how electrical connections are established which would appear to be possible in the factory only, given the complexity of the elements that are assembled together.
The present invention seeks to remedy those drawbacks, i.e. to provide an electronic module suitable for being fitted to the explosive stick so that the resulting assembly is certain to be operational and so that said assembly can be made simply using any standard detonator on the market.
To this end, in a first aspect, the invention provides an electronic module for a detonator, the module comprising an electronic circuit encapsulated in a mass of hardened resin in which there terminates at least one inlet conductor and from which there extend two outlet conductors forming a detonator ignitor line, the mass of resin being received in a tubular housing which extends beyond the mass of resin adjacent to the ignitor line to define a cavity. According to the invention, the outlet conductors are longer than the depth of the cavity and form a short-circuited ignitor line outside the mass of resin inside the cavity, which cavity is provided with a removable end cap.
This module which possesses no explosive material can be manufactured, handled, and transported without special precautions, and in any event without it being necessary to satisfy the requirements of regulations concerning explosive materials.
In addition, since the output conductors short circuit the ignition line at the outlet from the mass of resin, they constitute a single wire closed on the electronic circuit, which is advantageous in several respects. Firstly, since the outlet of the electronic circuit is short circuited, electrical continuity is established which makes it possible to proceed with various tests during manufacture without it being necessary to close the ignitor circuit. Secondly, the short circuit made at the outlet from the electronic circuit guarantees complete discharge of the capacitance which the electronic circuit includes in conventional manner as means for storing the electrical energy required for igniting the detonator. This guarantee that the energy storage means is completely discharged makes it possible to connect the electronic module to the detonator proper in complete safety.
Also in preferred manner, the cap of the module of the invention is made in the form of a plug of elastically deformable material and the means for holding the detonator are formed merely by a central orifice in the cap which enables the end of a detonator to be engaged therein by force. The use of a cap made of elastomer makes it possible, while holding the detonator, to ensure that the assembly of the explosive stick with the electronic module is leakproof and provides the electrical connections with protection from one another. Another advantage of an elastomer cap lies in its ability to receive detonators of different diameters in the central orifice merely because it is radially elastic.
Still in preferred manner, the cap has a head portion with at least one outside transverse dimension greater than the corresponding inside transverse dimension of the cavity of the tubular housing. In other words, if the tubular housing is cylindrical, then the cap has a head portion of diameter greater than the inside diameter of the cylinder so as to bear against the end of the cylinder via the outwardly-projecting head. Without going beyond the ambit of the invention, the section of the tubular housing could be polygonal.
In a second aspect, the invention provides a method of making an electronic delay detonator, the method consisting in assembling a standard detonator to a module for testing the above characteristics, which method consists in separating the housing from the cap, in engaging the detonator in the cap via its end provided with the ignitor conductors, in connecting the conductors of the detonator to the outlet conductors of the electronic circuit, and in replacing the cap fitted with the detonator in the cavity.
It will be understood from the description of the method, that the operations involved are extremely simple and can be performed quite safely on the site where the detonators are to be used.
Naturally, insofar as the ignition line at the outlet from the electronic circuit is formed by a single looped conductor, it is necessary to cut the loop in order to make the connection with the detonator.
Finally, in order to improve the safety of personnel who are to assemble the electronic module and the detonator, in a third aspect, the invention provides tooling for implementing the assembly method when the cap has a head portion as described above, which tooling is constituted by a bell for taking hold of the detonator fitted with the cap, said bell forming a pusher for engaging the cap in the cavity of the electronic module. Thus, an operator who has withdrawn the cap from the electronic module engages the detonator stick in the cap and then engages the assembly in the bell which encloses the detonator in a volume that is designed so that in the event of the detonator exploding in untimely manner, said explosion takes place inside the bell and the hand and forearm of the operator are protected. The operator makes the connections after the cap has been put into place in the bell, and the bell enables the operator to force the cap back into place in the housing containing the electronic circuit.